A Literature Review surveys scholarly source materials that are relevant to a person's research thesis/problem and/or a particular issue or theory. It also provides a critical analysis that summarizes and synthesizes the source materials while also demonstrating how a person's research pertains to or fits within the larger discipline of study.
Literature Reviews vary from discipline to discipline as well as across assignments, but generally a good literature review is designed to help you answer 2 questions:
What do we know about this particular issue, theory or subject?
What do we not know about this particular issue, theory or subject